U.S. Pat. No. 6,686,691 has disclosed a luminescence conversion LED, in which the primary light source used is a blue chip. A phosphor layer containing two phosphors, which absorb blue and emit green and red, is connected ahead of the chip. In this case, however, the two phosphors are distributed homogenously in the resin, which leads to undesirable effects. It is accordingly not possible to satisfy the two criteria of “high efficiency” and “good color rendering” simultaneously. To achieve a high color rendering, either a green phosphor which actually has too short a wavelength has to be used, with this then being shifted by the strong absorption of the red phosphor, or the red phosphor has to be shifted as far as possible toward a long wavelength. Both solutions reduce efficiency on account of the high absorption in the first case and the low visual utility of the red radiation component in the second case.
WO 00/33390 has disclosed a luminescence conversion LED in which the primary light source used is a blue chip. A phosphor layer comprising two phosphors which absorb blue and emit green and red is connected ahead of the chip. The two phosphors can be used as a mixture or as separate layers.
U.S. Pat. No. 6,642,652 and U.S. Pat. No. 6,696,703 have each disposed a luminescence conversion LED in which the primary light source used is a blue chip. Two phosphor layers which absorb blue and emit green and red are connected ahead of the chip. In this case, the red phosphor layer is arranged directly on the substrate and the green phosphor layer is located directly above the red phosphor layer.
US 2004/169181 has disclosed a thin-film LED with phosphor.